The present invention relates to exercise equipment of the type which utilizes one or more weights to apply a force to a movable handle.
Various types of exercise equipment are known wherein one or more weights are used to exert a gravitational force against a handle or the like which is moved by a user. For example, in one type of device, the handle is attached to one end of a pivot arm that allows the handle to be moved up or down by a user. A weight is either attached to the pivot arm between the pivot point and the handle, in which case the handle is forced downward by the gravitational force of the weight, or attached to the pivot arm on the opposite side of the pivot point, in which case the handle is forced upward as the weight is drawn downward by the gravitational force.
In another type of exercise equipment, the handle is attached to one end of a cable, called the proximal end, which may be pulled or released by a user. In this case, the weight is coupled to an opposite, distal end of the cable to apply a tensile force to the cable as it is pulled and released with the handle.
Equipment of this type operates extremely well to develop arm and/or leg muscles when the handle is pulled or pressed relatively slowly, thus moving the handle back and forth, in its two opposite directions of movement, in such a manner that the gravitational force applied to the handle remains substantially constant. However, such equipment does not maintain this constant gravitational force when the handle is moved rapidly back and forth by the user—an exercise known as “high-speed training”. In this case, the momentum developed by the weight during the high-speed movement creates an uncontrollable and sometimes dangerous variation in the force applied to the handle. In the case of machines with a pivoted traveling arm, the variation in gravitational force may be so great, as the arm switches directions, that it can be harmful to the user as he or she braces to try and hold on to the handle. Similarly, with machines which employ a cable connected to a weight, the weight can be caused to fly up along the guide rods, causing the tension in the cable to fall to zero, and then “bounce back” with a sudden jerk of the cable and a consequent spike in the cable tension, as the weight falls back down again and the cable brakes its descent.
Ideally, the force applied to the handle of exercise equipment should remain approximately constant, independent of the speed with which the handle is moved by the user. However, with high-speed training movements, the force due to weights varies considerably.
Exercise equipment is also known which does not use a weight or weights to apply a gravitational force to a user handle. Such equipment uses a set of elastic bands, springs, torsion bars or the like which apply a spring force to the handle. With such equipment, the static force applied to the handle is substantially the same as the dynamic force applied when the handle is moved, either slowly or rapidly. As compared to an exercise machine which employs a weight to apply a gravitational force to the handle, such machines have a disadvantage that the spring force increases linearly as the handle is moved from its rest position to an extended position. When the spring constant is relatively high, to provide a substantial spring force in the mid-range of movement of the handle, this force becomes extremely high as the handle is moved toward the end of its travel, just in a position where the user's arms or legs are extended and, consequently, their strength becomes weaker.
The U.S. Pat. No. 6,561,956 discloses a “dynamic active resistance training system” which comprises exercise apparatus of the type that incorporates a weight stack, with a selectable number of weights, which is lifted by a user by means of a cable. The proximal end of the cable is provided with a handle to be held and pulled by the user. The distal (opposite) end of the cable is attached to the weight stack. In addition to the weight stack, one or more “resiliently stretchable” cords are connected in parallel on one side of the weight stack, between the top most weight and the bottom of the frame of the exercise apparatus, to exert additional tension on the cable due to the spring force. While the arrangement disclosed in this patent is partially effective for the purpose for which it is intended, the application of force to one side of the weight stack causes the stack to become unbalanced, resulting in excessive friction and binding against the guide rails that provide lateral support to the movable weights. This increased friction impairs the operation of the exercise equipment especially when it is to be used in “high-speed training” where the handle is rapidly moved back and forth by the user.